We are continuing the study of several enzymes involved in either the degradative metabolism of vitamin B6 by organisms that use this vitamin as an energy and carbon source, or the interconversion of free and coenzyme forms of the vitamin. Among the first group of enzymes are: (1) An FAD and NADPH-requiring dioxygenase from an Arthrobacter sp. that cleaves the pyridine ring of 2-methyl-3-hydroxyl-4-hydroxymethyl-pyridine-5-carboxylic acid. This enzyme appears to differ in subunit structure from an analogous enzyme from Pseudomonas sp. MA we have studied extensively in previous years. (2) 4-Pyridoxic acid dehydrogenase from Pseudomonas sp. MA. We hope to establish the nature of the electron acceptors in this interesting membrane-bound enzyme. Among the second group of enzymes is pyridoxine dehydrogenase. This homogeneous enzyme from yeast needs further characterization with respect to subunit structure and its role in vitamin B6 metabolism. Finally we are attempting to clarify the process by which histidine prodecarboxylase from mutant 3 of Lactobacillus sp. 30a is converted to the active decarboxylase. We will also begin work directed at determining the amino acid sequence of this enzyme.